Attacking and blocking creatures that have first strike and double strike deal combat damage before other creatures. Then, all creatures except those with first strike deal combat damage.Creatures that have double strike deal combat damage twice each combat.It's possible for a creature to be destroyed before it can deal its combat damage.

You can play the skill quest "First Strike" to see how this game concept works.

Normally, all attacking and blocking creatures deal combat damage at the same time. However, a creature with first strike deals its combat damage first, before creatures without first strike. This means a creature with first strike can often destroy an enemy creature before that creature gets the chance to hit back.Well done! First strike is advantageous on both offense and defense.

702.7a First strike is a static ability that modifies the rules for the combat damage step. (See rule 510, “Combat Damage Step.”)

702.7b If at least one attacking or blocking creature has first strike or double strike (see rule 702.4) as the combat damage step begins, the only creatures that assign combat damage in that step are those with first strike or double strike. After that step, instead of proceeding to the end of combat step, the phase gets a second combat damage step. The only creatures that assign combat damage in that step are the remaining attackers and blockers that had neither first strike nor double strike as the first combat damage step began, as well as the remaining attackers and blockers that currently have double strike. After that step, the phase proceeds to the end of combat step.

702.7c Giving first strike to a creature without it after combat damage has already been dealt in the first combat damage step won’t prevent that creature from assigning combat damage in the second combat damage step. Removing first strike from a creature after it has already dealt combat damage in the first combat damage step won’t allow it to also assign combat damage in the second combat damage step (unless the creature has double strike).

702.7d Multiple instances of first strike on the same creature are redundant.[1]

When Combustible Gearhulk enters the battlefield, target opponent may have you draw three cards. If the player doesn't, put the top three cards of your library into your graveyard, then Combustible Gearhulk deals damage to that player equal to the total converted mana cost of those cards.

Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)
Whenever Consul's Lieutenant attacks, if it's renowned, other attacking creatures you control get +1/+1 until end of turn.

When Knight of the White Orchid enters the battlefield, if an opponent controls more lands than you, you may search your library for a Plains card, put it onto the battlefield, then shuffle your library.

Kor Bladewhirl (2)Creature — Kor Soldier Ally (2/2)Rally — Whenever Kor Bladewhirl or another Ally enters the battlefield under your control, creatures you control gain first strike until end of turn.

Other Minotaurs you control have first strike.
As long as you have one or fewer cards in hand, Minotaurs you control get +2/+0.
Whenever Neheb, the Worthy deals combat damage to a player, each player discards a card.

Whenever Reckless Racer becomes tapped, you may discard a card. If you do, draw a card.

Rhet-Crop Spearmaster (3)Creature — Human Warrior (3/1)You may exert Rhet-Crop Spearmaster as it attacks. When you do, it gets +1/+0 and gains first strike until end of turn. (An exerted creature won't untap during your next untap step.)

Whenever a Vampire you control deals combat damage to a player, put a +1/+1 counter on it.
Madness (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Toolcraft Exemplar (1)Creature — Dwarf Artificer (1/1)At the beginning of combat on your turn, if you control an artifact, Toolcraft Exemplar gets +2/+1 until end of turn. If you control three or more artifacts, it also gains first strike until end of turn.

Veteran Warleader (3)Creature — Human Soldier Ally (*/*)Veteran Warleader's power and toughness are each equal to the number of creatures you control.

Tap another untapped Ally you control: Veteran Warleader gains your choice of first strike, vigilance, or trample until end of turn.